PGT

hi peeps

does anyone know if there is any correlation between cfm and bhp?

if so how many cfm is 400bhp

PGT

bttt

SeanT

it does depend, a head could only flow 150 cfm but make 400 BHP relatively easy with 2 bar of boost (like a totally standard cossie on a T34, greys for example) or it could flow well over 200 cfm and make the same power with 21 psi (these are examples, i only really know about aspirated shit)

Normally aspirated, you'd need either a lot of ccs, a lot of revs, and a head / heads and induction system that flow at least 250 cfm to make 400 bhp afaik

My numbers are gonna be miles out!!

dave green

cfm. I thuoght cfm stood for cubic foot per minute. relates to air compressors.
could be completly wrong, but never heard of engine power measured in cfm


Dave

SeanT

the amount a venturi will flow is measured in cfm, so it relates directly to head porting and inlet manifolds, carbs etc. in that way.
The yanks measure their four barrel carbs in cfm rather than in actual size like the eyeties do Ie. a 600 Holley will flow 600 cubic feet per minute of air at wide open throttle, when attached to a big enough engine to do this!!!

Of course, it only relates to how much air can flow, not how it flows
Who says head porting is a black art

PGT

but if 600 cfm (at atmospheric pressure and say 20c) goes into the holley air filter (or equally into the air filter on a turbo engine) and assumming the fuel mixture is correct, is there not a direct relationship between cfm and bhp??

anyone??

SeanT

Could depend couldn't it..... how much of it is shoved back out of the exhaust, do the valves open wide and for long enough for all of it to get into the combustion chamber in the first place, and can the routes that the air must travel flow the required amount in the time that the valve is open.

The engine sucks the air in through the carb, getting the air in is the really important part, which is why super/turbo charging is so damn effective!

hexxon

This is much more complicated an issue than what some may sound it to be. There is a relationship between cfm and bhp. This is however depending on a huge amount of factors such as, to state a few examples, volumetric efficiency, brake specific fuel consumption, engine volume, rpm of maximum power output et.c.

As far as heads concerned, just making a head flow 400 cfm sure as hell wont guarantee to make it flow well in an engine. The problem is to make the head flow well through all stages of cam lift, air velocity, air density and humidity. Now thats black art. It doesnt boil down to total amount of flow when it comes to horsepower, it boils down to volumetric efficiency.

SeanT

Agreed
It is still how heads are measured, air flow at different amounts of lift, but the engine has to be designed to work as a whole